The exceptionally solar and geomagnetic quiet winter of 2019–2020 provides a very useful scenario to study polar mesospheric radar echoes. Such a condition limits the impact of ionisation caused by geomagnetic storms and particle precipitation and allows to investigate the role of moderate electron densities as well as neutral dynamics in formation and transport of the structures causing these echoes. For this purpose we used the continuous operation of the sensitive VHF Middle Atmosphere Alomar Radar System (MAARSY) in conjunction with the Saura partial reflection radar throughout the winter as key instruments to monitor the Mesosphere. Eight months of radar measurements are analyzed in respect to occurrence, echo power, spectral widths and their relation to practically common volume measurements of electron densities. VHF polar mesospheric echoes observed during 2019/2020 were generally more faint and occurred less frequent than in previous year. The very low occurrence rates of 6.5% at most for the months November to February as well as the complete absence of echoes below 56 km throughout the season are very remarkable. Highest occurrences of echoes with spectral widths mostly below 3 ms⁻¹ were seen for electron densities of 3 ⋅ 10⁸ m⁻³, while on average Ne ~ 5.5⋅ 10⁸ m⁻³ were observed for the presence of VHF echoes, representing a necessary prerequisite to observe such VHF radar echoes. VHF radar echoes occurring at altitudes below 75 km furthermore seem to show preferences to distinct electron number density windows.

2019-2020 年异常的太阳和地磁安静冬天为研究极地中间层雷达回波提供了非常有用的场景。这种条件限制了由地磁暴和粒子降水引起的电离的影响，并允许研究中等电子密度以及中性动力学在引起这些回波的结构的形成和传输中的作用。为此，我们在整个冬季使用灵敏的 VHF 中层大气 Alomar 雷达系统 (MAARSY) 和 Saura 部分反射雷达的连续运行作为监测中层的关键仪器。对八个月的雷达测量进行了分析，涉及发生、回波功率、谱宽及其与实际常见的电子密度体积测量的关系。与前一年相比，2019/2020 年观测到的甚高频极地中间层回波通常更微弱，发生频率也更低。11 月至次年 2 月最多 6.5% 的极低发生率以及整个季节 56 公里以下完全没有回波是非常显着的。频谱宽度大多低于 3 ms 的回波出现次数最多^-1的电子密度为 3 ⋅ 10 ⁸  m ^-3，而平均 Ne ~ 5.5⋅ 10 ⁸  m ^-3被观察到 VHF 回波的存在，这是观察此类 VHF 雷达回波的必要先决条件。此外，发生在 75 公里以下的 VHF 雷达回波似乎显示出对不同电子数密度窗口的偏好。